1. Field of the Invention
This invention relates to a method of producing a novel conjugated diene polymer having excellent wear resistance and mechanical properties and a reduced cold flow by polymerizing a conjugated diene compound with a catalyst of rare earth element compound and reacting the resulting polymer just after the polymerization with at least one compound selected from the group consisting of a halogenated organometallic compound, a halogenated metal compound, an organometallic compound, a heterocumulene compound, a hetero three-membered-ring containing compound, a halogenated isocyano compound, a carboxylic acid, an acid halide, an ester compound, a carbonic ester compound, an acid anhydride and a metal salt of a carboxylic acid as a modifying agent.
2. Description of Related Art
Since conjugated diene polymers play an industrially very important role, there have hitherto been proposed many proposals on a polymerization catalyst for a conjugated diene compound in the production of the conjugated diene polymer. Particularly, many polymerization catalysts giving a high content of cis-1,4-bond have been studied and developed for providing conjugated diene polymers having high performances in the thermal and mechanical properties. For example, there are well-known composite catalyst systems containing a compound of a transition metal such as nickel, cobalt, titanium or the like as an essential component. Among them, some catalysts have industrially and widely been used as a polymerization catalyst of butadiene, isoprene or the like (see End. Ing. Chem., 48, 784(1956) and JP-B-37-8198).
On the other hand, a composite catalyst system comprising a rare earth metal compound and an organometallic compound of an element of Group I-III has been studied and developed in order to attain a further higher content of cis-1,4-bond and an excellent polymerization reactivity, and also studies on a high stereospecific polymerization using the same have been actively conducted (see Makromol. Chem. Suppl., 4, 61(1981), J. Polym. Sci, Polym. Chem. Ed., 18, 3345(1980), a specification of German Patent Application No. 2,848,964, Sci, Sinica., 2/3, 734(1980) and Rubber Chem. Technol., 58, 117(1985)).
Among these catalyst systems, a composite catalyst consisting essentially of a neodymium compound and an organoaluminum compound has been confirmed to provide a high cis-1,4-bond content and an excellent polymerization reactivity and has already been industrialized as a polymerization catalyst for butadiene or the like (see Macromolecules, 15, 230(1982) and Makromol. Chem., 94, 119(1981)).
However, a commercial demand on polymers becomes higher with the advance of recent industrial technique and also it is strongly demanded to develop polymer materials having higher wear resistance, mechanical properties and thermal properties (thermal stability and the like).
As an effective means for solving the above problem, there are actively conducted research activities on a polymerization method exhibiting a high polymerization reactivity toward a conjugated diene compound and capable of providing a narrow molecular weight distribution to the resulting polymer.
For example, it is known to increase the polymerization reactivity when using a two-component system consisting of a neodymium compound and methylaluminoxane (see Polymer Communication, 32, No. 17, p514(1991)). Furthermore, it is reported that a conjugated diene polymer having a narrow molecular weight distribution is obtained under a high polymerization reactivity when using a catalyst system produced by adding an organoaluminum compound and/or a Lewis acid to the system of neodymium compound and aluminoxane (see JP-A-6-211916, JP-A-6-306113 and JP-A-8-73515). However, the polymers obtained by the above polymerization methods are generally straight-chain polymers being less in the branched structure, so that they may have a problem on the mixing property or processability with a polymer material such as rubber, or various fillers in accordance with applications, and are large in the cold flow to cause troubles in the storing and transportation.
In JP-A-63-178102, JP-A-63-297403, JP-A-63-305101, JP-A-5-51406 and JP-A-5-59103 are reported polymers having improved processability obtained by polymerizing a conjugated diene compound in a catalyst system consisting of a neodymium compound and an organoaluminum compound and then reacting with a specified compound as a coupling agent. However, the polymerization reactivity in such a catalyst system is not sufficiently satisfied.